Implementations of the claimed invention generally may relate to the field of power supplies, and in particular to a mode transition scheme for a load-adaptive power converter.
The power loss of a DC/DC voltage regulator (VR) or a switching mode power converter/inverter (e.g. a pulse width modulated power converter) may include three components including, for example, switching loss, conduction loss and gate driver loss. In general, in order to reduce the total power loss, the switching loss and gate driver loss are lower at a lower switching frequency. However, the ripple voltage/current may increase as the switching frequency decreases. For a particular application, tradeoffs may be made based on load demands and component parasitics. In a light load, for example during a discontinuous conduction mode (DCM), a lower switching frequency (fixed or variable) may be utilized since the switching loss may be dominant and the conduction loss may be relatively small. In a medium or heavy load, for example during a continuous conduction mode (CCM), a fixed and higher switching frequency may be applied due to increasing conduction loss, including the ripple voltage/current, with a load current.
Various techniques may utilize both DCM and CCM to improve overall efficiency. In a Mode-Hopping technique, the DC-DC Buck VR for example operates in synchronous mode at CCM (Continuous Conduction Mode) at high load demand while the inductor current does not go below zero and operates in asynchronous mode at DCM (Discontinuous Conduction Mode) when the inductor current starts approaching the zero amperes point to reduce mainly conduction losses. In a Pulse-Skipping or variable switching frequency technique the VR switching frequency is lowered as the load becomes smaller to reduce mainly switching losses and can be implemented by using hysteretic control or variable frequency PWM control.
Both of these techniques result in efficiency improvement especially at light load. An issue with both the Mode-Hopping and Pulse-Skipping technique is that the output voltage ripple may increase during a transition between the CCM and DCM operation, which in some applications may exceed a maximum supply voltage deviation required by the load and increase the equivalent series resistance (ESR) power loss.